Clad metal contacts for reed switches



Feb. 24, 1970 J. A. RIFF GLAD, METAL CONTACTS FOR REED SWITCHES Filed Jan. 10, 1968 F K52 F|G I2 20 SILVER CADMIUM OXIDE I SILVER I /I8 NOBLE METAL CLAD aoun BASE METAL NICKEL-IRON l |4 as ZIO 227 f2] QT +4 --+-4 FIG.6

INVENTOR JAMES A. RIFF BY'ZH 72M ATTORNEYS.

United States Patent 3,497,655 CLAD METAL CONTACTS FOR REED SWITCHES James A. Riff, Chicago, Ill., assignor to Motorola, Inc., Franklin Park, TIL, a corporation of Illinois Filed Jan. 10, 1968, Ser. No. 696,825 Int. Cl. HOlh 3/00, 9/00; Hillr 9/02 U.S. Cl. 200-166 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The invention pertains to the construction of the cantilevers of a reed-type switch.

Two well known problems presently hamper the operation and life of reed switches. Both of these problems are related to the fact that the cantilevers of most reed switches made today meet in only one contact surface. For instance, when contact is broken between the cantilevers upon opening the switch, an arc is drawn between the two contact surfaces at the single point of contact, and if the current through the cantilevers is sufiicient, it welds the two contacts together rendering the switch inoperable. Even if the current is insufficient to weld the contacts, it can cause pitting and oxidation of the contact surfaces. This oxidation causes a high resistance area to form on the contacts severely limiting the operation of the switch.

In addition, with the contacts closed and a high current passing through the switch, a great amount of heat is generated in the cantilevers, which can also cause oxidation of the contact surfaces.

Furthermore, present practices for manufacturing the cantilevers for reed switches have generally resulted in great waste of valuable metal. It is common within the reed switch industry today to stamp the cantilevers from a sheet of base metal and subsequently electroplate the stamped cantilevers on all surfaces in a solution of a noble metal to form the contact surface. Because only one surface of each cantilever actually makes contact between the members, the contact material plated on the remaining parts of the cantilever is Wasted.

SUMMARY OF THE INVENTION It is an object of this invention to provide cantilever members for a reed switch that are constructed in a manner which prevents welding of the cantilevers to one another upon drawing an are between the members with the opening of the switch.

It is another object of this invention to reduce the possibilities of high current passing through the cantilever members causing oxidation of the contact surfaces.

It is a further object of this invention to provide material for the construction of the cantilevers of a reed switch, which provides for the positioning of the noble metal on only the contact surface thereby reducing costs.

In one embodiment of this invention a copper centered nickel-iron wire is formed into a sheet of rectangular stock. Subsequently, a sheet of silver is clad to one surface of the stock, and cadmium is then difiused into the silver to form an exposed layer of silver cadmium oxide, which acts as the contact surface. The individual cantilevers or reeds are sheared from the composite material. By using a cladding process only the contact surface of the cantilever is covered with the valuable silver and silver cadmium oxide layers. Silver cadmium oxide, once it is diffused in the silver, will not weld to itself when the two cantilevers are separated on opening the switch, any are drawn between the two members will not weld them together. The copper core of each of the cantilevers conducts heat to the relatively heavy mass of the leads connected to the cantilevers where it is dissipated.

Therefore, heat in the cantilever members resulting from high current passing through the cantilevers with the switch closed is removed by the copper core thereby reducing the possibilities of oxidation of the contact surfaces.

Cladding of the silver to the nickel iron sheet permits configurations for the contact surfaces of the cantilevers which were not possible using the conventional stamping or forming methods. For instance, in one embodiment one cantilever has a relatively flat contact surface while the other cantilever has a contact surface .in the form of first and second rail portions clad to the base metal so that when the switch is closed the cantilevers are engaged at two distinct points. In another embodiment, one cantilever has an arcuate contact portion and is thinner than the other member of the pair. The other member has the silver clad to the base metal in the form of a V-shaped block so that the arcuate portion engages the block in two points on each side of the V to form a two point contact. The two point contact acts to dissipate the are when the switch is open thereby reducing pitting and oxidizing of the contact surfaces.

DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates metal stock made in accordance with this invention in the form of a plate;

FIG. 2 illustrates a second metal block made in accordance with this invention in the form of a plate;

FIG. 3 illustrates a reed switch in accordance with this invention;

FIG. 4 is a front view in cross-section along the line 44 of FIG. 3, illustrating a set of cantilevers for a reed switch in accordance with this invention;

FIG. 5 is a front view in cross-section of a different set of cantilevers for a reed switch in accordance with this invention; and

FIG. 6 is a front view in cross-section of still a further set of cantilevers for a reed switch in accordance with this invention.

The term clad as used in this application means the manufacturing of composite metals by a process in which no liquid phase is present at the bond line. An example of such a process is cold welding, which consists essen tially of pressing localized areas under extremely heavy pressure to cause great local deformation and welded spots.

DETAILED DESCRIPTION Referring to the figures of the drawings, FIG. 1 illustrates the basic concept of a composite electrically connecting material for forming the cantilevers or reeds of a reed switch. Essentially, a base layer 10 of a metal having a high permeability is selected from the group consisting of iron, nickel, nickel-iron, nickel cobalt, cobalt iron and nickel cobalt iron. A second layer 12 of noble metal is clad to the base metal to form a single exposed contact surface. The noble metal can be selected from the group consisting of silver, gold and platinum. By using a metal cladding process it is possible to position the noble metal on only a single surface of the base metal so that only the contact surface will contain the noble metal While the remaining surfaces of the base metal remains exposed. The economic advantages of realizing the significance of cladding a metal to form a single contact surface on the base metal over those switches where the contact metal is plated on all surfaces of the base metal is readily apparent.

FIG. 2 illustrates one example of the specific make-up of sheet material from which the cantilevers or reed switches may be made. Rectangular stock of commercially available, copper centered nickel-iron forms the base metal 14 of the sheet which has a copper core 16. In the next step a sheet of silver is clad to the nickel-iron surface. Subsequently, cadmium is diffused into the silver to form an exposed layer 18 of silver cadmium oxide 20. In this instance, silver was selected to be clad to the nickeliron base metal so that the cadmium could be diffused into the silver to form the silver cadmium oxide layer the advantages of which will be described subsequently.

FIG. 3 illustrates a typical contact-type reed switch hav* ing a first cantilever 22 and a second cantilever 24. At least one of the cantilevers is actuable in response to a magnetic field to engage the contact surfaces of the cantilevers in order to close the switch. Removal of the magnetic field from the switch causes the cantilevers to break contact to open the switch. Connected to each of the can tilevers 22 and 24 respectively are copper wires 26 and 28 which connect the cantilevers to an electrical circuit. The reed tube 21 preferably is filled with an arc quenching gas such as sulfur-hexafiuoride (SP which acts to prevent aging of the contacts.

The cantilevers 22 and 24, shown in cross-section in FIG. 4, have each been sheared from a sheet of the material described in connection with FIG. 2. Each of the contacts are rectangular in shape, and the silver cadmium oxide surfaces 18 and 18a are relatively flat so that the shape of the cantilevers generally conform to the configuration of the cantilevers well-known in the art. The diffused silver cadmium oxide contact surfaces 18 and 18a however, provide an important advantage over the prior art cantilevers. In prior art devices, breaking the contact between the cantilevers when open circuiting the switch, causes an arc to be drawn between the two cantilever members which in addition to pitting and oxidizing the contact surfaces can result in welding of the two contacts together, providing the current is sufliciently great. The two contact surfaces 18 and 18a of silver cadmium oxide, however, will not weld to each other when a high current are is drawn therebetween. This, of course, results in reliable operation of the switch under high current applications.

The copper cores 16 and 16a in the base metal layers 14 and 14a of the cantilevers 24 and 22 also makes a notable advance in reed switch development. For one thing the copper centers provide more flexible cantilevers so that they are extremely sensitive to the magnetic fields. In addition although the copper has the desired property of being an excellent electrical conductor, it is also a good heat conductor. In prior art devices, when reed switches have been closed for long periods of time under high current conditions, the cantilevers heat up and the metal reaches its Curie point. At this point the metal loses its magnetic properties and the cantilevers open. By using the copper cores taught by this invention, however, the heat from the cantilevers is transferred through the copper cores 16 and 16a, respectively, to the wire leads which, having relatively greater mass, tend to dissipate the heat from the cantilever members thereby greatly reducing the possibility of the cantilevers opening at an inopportune time.

FIGS. and 6 emphasize the advance in the art made by the application of cladding principles to the manufacture of cantilevers for reed switches. FIG. 5, shows a crosssection view, similar to that of FIG. 4, of a pair of cantilevers 30 and 32 in a reed switch. Cantilever 30 is constructed from a plate similar to that described in connection with FIG. 2 and has the same general flat rectangular cross-section, as the conventional geometric shapes for cantilevers illustrated in FIG. 4. The cantilever includes a base metal of nickel-iron 32, which has a core 34 of copper. A layer of silver 36 is clad to the base metal 32. Cadmium is diffused into the silver layer to form a layer 38 of silver cadmium oxide for the flat contact surface. The configuration of cantilever 32 differs considerably, however, from the conventional shape of cantilevers. The cantilever 32 includes a base metal of nickel-iron 40, which has a copper core 42 similar to cantilever 30. In this cantilever, however, two rails of silver 44 and 46 are clad down either side of the rectangular base metal for the longitudinal length of the cantilever. Cadmium is then fused into the silver to form first and second contact portions 48 and 50 of silver cadmium oxide. In operation, when the cantilevers are moved into contact in response to the application of the magnetic field, each of the rails 48 and 50 engages the contact surface 300 of the cantilever 30 so that there is a two point contact between the cantilever members 30 and 32. When the magnetic field is removed and the contacts open, any are drawn between the two cantilever members is distributed between the two points of contact rather than one point thereby greatly reducing pitting and possible oxidation of the contact surface by the arcing.

FIG. 6 illustrates a further embodiment of the cantilevers for a reed switch which incorporates an additional geometric configuration made possible by the cladding process. In this embodiment, cantilever is of less width than cantilever 62. Cantilever 60 is constructed of sheet material with a nickel-iron base layer 64, which has a copper core 66 therein. A layer of silver 68 is clad onto the base metal 64 in an arcuate configuration. Cadmium is then diffused into the silver layer 68 to form an arcuate contact portion of silver cadmium oxide 70. The cantilever 62 likewise has a base layer of nickel-iron 72 in which is located a copper core 74. A layer of silver 76 is clad onto the metal base 72 in the form of a V-shaped block. Cadmium is then diffused into the silver layer 76 to form a layer of silver cadmium oxide 78, which provides a V-shaped contact surface for the cantilever member 62. When the cantilever 60 is engaged with the cantilever 62, the arcuate contact portions of the cantilever 60 engages the opposite sides of the V-shaped contact surface 78 so that contact is made at two points between the members. The advantages gained from this two point contact are the same as those described for the embodiment shown in FIG. 5.

What has been described is a unique and relatively inexpensive construction of a cantilever for a reed switch which greatly reduces pitting and oxidizing of the contact surface and the possibility of the cantilever members being welded together upon opening the switch.

What is claimed is:

1. Composite electrically conducting material for forming the cantilevers of a reed switch, the combination in cluding, a plurality of metal layers comprising a base layer of a metal having a high permeability selected from the group consisting of iron, nickel, nickel-iron, nickel cobalt, cobalt iron and nickel cobalt iron, said base layer having a copper core, and an exposed layer of noble metal selected from the group consisting of silver, gold and platinum clad to said base layer to form a contact surface portion.

2. The electrically conducting material of claim 1 wherein said exposed layer is silver clad to said base layer, and the material further includes a layer of silver cadmium oxide diffused into said layer of silver to form the contact surface.

3. In a reed switch having first and second cantilevers at least one of which is actuable in response to a magnetic field to respectively engage the cantilevers and open the connection between the same for operating the switch,

the combination including, each cantilever comprising a base layer of a metal having a high permeability selected from the group consisting of iron, nickel, nickel-iron, nickel cobalt, cobalt iron and nickel cobalt iron, said base layer metal having a core of copper, a second layer of silver clad to said metal of the base layer, and an exposed layer of silver cadmium oxide diffused into said silver layer to form a contact surface, said silver cadmium oxide layer preventing said contact surfaces from Welding together with the drawing of an arc between said contact surfaces with the opening of the cantilevers, said copper core acting as a heat conductor to remove heat from said contact surfaces to protect the same from oxidation.

4. The reed switch of claim 3 wherein said contact surface of one of the cantilevers is relatively flat, and said contact surface of the other cantilever includes first and second rail portions extending longitudinally of the cantilever, said first and second rail surfaces engaging said relatively flat surface to form a two point contact with the cantilevers being engaged and acting to reduce oxidation of said contact surfaces and prolong life of the reed switch with an arc being drawn by the cantilevers with the same being opened.

5. The reed switch of claim 3 in which the width of the first cantilever is less than the width of the second cantilever, and wherein said contact surface of the first cantilever includes an arcuate portion, and said contact surface of the second cantilever includes a V-shaped block, said arcuate contact surface engaging respective sides of said V-shaped contact surface to form a two point contact with the cantilevers being engaged, so that the are drawn by the cantilevers with the same being opened is distributed between said two points of contact to reduce oxidation of said contact surfaces thereby prolonging the life of the reed switch.

References Cited UNITED STATES PATENTS 2,722,584 11/1955 Skay. 3,078,562 2/1963 Gwyn et al. 3,113,196 12/1963 Spooner et a1. 3,151,385 10/1964 Gwyn. 3,152,237 10/1964 Richert et al. 3,249,728 5/ 1966 Sasamoto et al. 3,288,971 11/ 1966 -Polleys. 3,316,513 4/1967 Bradford.

HERMAN O. JONES, Primary Examiner US. Cl. X.R. 29630 

